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.Dd $Mdocdate: November 2 2019 $
.Dt CMS_ENCRYPT 3
.Os
.Sh NAME
.Nm CMS_encrypt
.Nd create a CMS EnvelopedData structure
.Sh SYNOPSIS
.In openssl/cms.h
.Ft CMS_ContentInfo *
.Fo CMS_encrypt
.Fa "STACK_OF(X509) *certificates"
.Fa "BIO *in"
.Fa "const EVP_CIPHER *cipher"
.Fa "unsigned int flags"
.Fc
.Sh DESCRIPTION
.Fn CMS_encrypt
creates a CMS
.Vt EnvelopedData
structure, encrypting the content provided by
.Fa in .
.Pp
The recipient
.Fa certificates
are added as
.Vt KeyTransRecipientInfo
structures by calling the function
.Xr CMS_add1_recipient_cert 3
internally.
Only certificates carrying RSA, Diffie-Hellman or EC keys are supported
by this function.
The
.Fa certificates
argument can be set to
.Dv NULL
if the
.Dv CMS_PARTIAL
flag is set and recipients are added later using
.Xr CMS_add1_recipient_cert 3
or
.Xr CMS_add0_recipient_key 3 .
.Pp
.Fa cipher
is the symmetric cipher to use.
It must support ASN.1 encoding of its parameters.
.Xr EVP_des_ede3_cbc 3
(triple DES) is the algorithm of choice for S/MIME use because most
clients support it.
.Pp
Many browsers implement a "sign and encrypt" option which is simply an
S/MIME
.Vt EnvelopedData
containing an S/MIME signed message.
This can be readily produced by storing the S/MIME signed message in a
memory BIO and passing it to
.Fn CMS_encrypt .
.Pp
The following flags can be passed in the
.Fa flags
parameter:
.Bl -tag -width Ds
.It Dv CMS_TEXT
MIME headers for type text/plain are prepended to the data.
.It Dv CMS_BINARY
Do not translate the supplied content into MIME canonical format
even though that is required by the S/MIME specifications.
This option should be used if the supplied data is in binary format.
Otherwise, the translation will corrupt it.
If
.Dv CMS_BINARY
is set, then
.Dv CMS_TEXT
is ignored.
.It Dv CMS_USE_KEYID
Use the subject key identifier value to identify recipient certificates.
An error occurs if all recipient certificates do not have a subject key
identifier extension.
By default, issuer name and serial number are used instead.
.It Dv CMS_STREAM
Return a partial
.Vt CMS_ContentInfo
structure suitable for streaming I/O: no data is read from the BIO
.Fa in .
Several functions including
.Xr SMIME_write_CMS 3 ,
.Xr i2d_CMS_bio_stream 3 ,
or
.Xr PEM_write_bio_CMS_stream 3
can be used  to finalize the structure.
Alternatively, finalization can be performed by obtaining the streaming
ASN1
.Vt BIO
directly using
.Xr BIO_new_CMS 3 .
Outputting the content of the returned
.Vt CMS_ContentInfo
structure via a function that does not properly finalize it
will give unpredictable results.
.It Dv CMS_PARTIAL
Return a partial
.Vt CMS_ContentInfo
structure to which additional recipients and attributes can
be added before finalization.
.It Dv CMS_DETACHED
Omit the data being encrypted from the
.Vt CMS_ContentInfo
structure.
This is rarely used in practice and is not supported by
.Xr SMIME_write_CMS 3 .
.El
.Sh RETURN VALUES
.Fn CMS_encrypt
returns either a
.Vt CMS_ContentInfo
structure or
.Dv NULL
if an error occurred.
The error can be obtained from
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr CMS_add0_cert 3 ,
.Xr CMS_add1_recipient_cert 3 ,
.Xr CMS_ContentInfo_new 3 ,
.Xr CMS_decrypt 3
.Sh STANDARDS
RFC 5652: Cryptographic Message Syntax (CMS)
.Bl -dash -compact -offset indent
.It
section 6.1: EnvelopedData Type
.It
section 6.2.1: KeyTransRecipientInfo Type
.El
.Sh HISTORY
.Fn CMS_encrypt
first appeared in OpenSSL 0.9.8h
and has been available since
.Ox 6.7 .
.Pp
The
.Dv CMS_STREAM
flag first appeared in OpenSSL 1.0.0.
